In modem mobile telephone systems, each mobile telephone typically includes a replaceable user-identity module, such as subscriber identification module (SIM), which is typically plugged into a mobile telephone when the mobile telephone is taken into use. In this regard, a SIM can typically store any of a number of different data identifying the subscriber, or user, of the mobile telephone, such as a telephone number assigned to the subscriber. In practice, the data can be used to check the user rights of the subscriber each time the user of the mobile telephone uses the services of the system. As the SIM typically includes the data identifying the user, by using the SIM, the subscriber can use any mobile telephone that operates in the system. If no arrangement existed by which misuse could be prevented, then, for example, mobile telephones that have been stolen, lost or otherwise misplaced would be easy to use by anyone possessing a SIM. Therefore, for example, in the GSM system, an international mobile equipment identification (IMEI) code is stored in a permanent memory location in each mobile telephone. The intent is that operators maintain a corresponding equipment identification register, EIR, which contains a list of the equipment identification codes of stolen telephones, for example.
In certain situations, the system checks the equipment identification code of the mobile telephone and compares it with the data in the equipment register. If the equipment is listed as stolen, the system should block its use. In the example GSM system, which is used quite broadly, it has not yet been possible to satisfactorily implement such a checking system. The equipment registers of the operators and the data contained therein are incomplete, and it is not possible in all networks to prevent the use of a stolen mobile telephone, even if it were noticed that it is stolen. Because the inadequacy of the system that prevents misuse is known by many people, mobile telephones are commonly stolen and misused. Further, because the GSM system and the amount of mobile telephones used in the system are continuously growing rapidly, it is probable that these problems will also exist in the future.